1. Field of the Invention
The present invention generally relates to energy metering, and more specifically, relates to a load control means utilized in energy metering applications.
2. Related Art
Energy meters have evolved from the early mechanical meters to solid state meters. Among other advantages, solid state energy meters provide power utility companies with increased flexibility in implementing various rate schedules. More particularly, the solid state energy meters provide increased functionality, such as time keeping, than previous mechanical meters. The meter time keeping function is used, for example, to implement a time-of-use rate schedule.
With a time-of-use rate schedule, the amount of energy consumed during predefined time periods is determined and stored in the meter. The utility company collects such data for billing purposes. In addition to billing a consumer for the total energy used, the utility takes into consideration the time and date when the energy was used.
For example, a utility may define two time periods--from 9:00 a.m. to 8:00 p.m. (Time Period I) and from 8:00 p.m. to 9:00 a.m. (Time Period II). The utility charges a higher rate for each unit of energy used in Time Period I and a lower rate for each unit of energy used in Time Period II. It should be understood, of course, that the above time periods are merely provided by way of example and such time periods typically vary from location to location. The general reasoning for such an approach to billing is that it is more expensive to provide energy during Time Period I (a higher energy usage period) than in Time Period II (a lower energy usage period). Particularly, in order to satisfy consumer energy needs during the high energy use period (Time Period I), more generating power and high voltage rated transformers and lines must be provided.
To reduce energy bills, consumers are encouraged to control the time at which energy is used. Load control devices are used for controlling time of energy usage. An example of an apparatus which can be utilized as a load control device is set forth in U.S. patent application Ser. No. 07/505,287, Late Point Optical Output For Electronic Meter (abandoned in favor of continuation U.S. patent application Ser. No. 07/989,993). which is assigned to the present assignee.
The domestic water heater is probably the most common load controlled in this manner. Particularly, since it is less expensive to heat the water in the hot water heater during the off-peak energy demand time, the load control device prevents energy from being supplied to the hot water heater during the peak demand time period.
Usually a watthour meter in conjunction with a time switch is employed in order that the load may be disconnected during the time of system peak demands. The time switch, for example, may be a time-controlled relay which "opens" during the peak demand time periods and "closes" during the off-peak demand periods. In this manner, energy used for the hot water heater is controlled.
It has been found that relays, if subjected to cycling temperature and humidity prior to installation, may not initially properly operate. It is therefore desirable to be able to test the operation of the relay immediately after installation. With known solid state meters, however, the load control function is controlled by computer code stored in the meter's electronic memory. Access to such code typically can only be obtained by using electronic programmer devices. It would be desirable to provide a simple mechanism to facilitate testing of the load control function without requiring electronic programmer devices or other special tools.
Further, in order to access and test a load control mechanism, it may be necessary to remove the meter cover. When removing a meter cover, however, it is possible that seals which protect the meter components from the external environment may be broken. It would be desirable to enable testing of the load control mechanism without removal of the meter cover.
Moreover, with such a load control mechanism, a customer may not be able to obtain hot water during the peak demand periods. If the water stored in the hot water heater has cooled, the customer would have to wait until the off-peak demand time period to obtain hot water. Having to wait for hot water can become very frustrating. It would be desirable, therefore, to provide a simple and easy to use mechanism so that a customer can override the load control mechanism.
Additionally, if a failure occurs, e.g., the hot water heater breaks down, a customer cannot get hot water when expected. If a service person is dispatched to the customer's house during the peak energy demand time period, however, the water heater is normally de-energized due to the operation of the load control means. The service person therefore must override the load control means so that the hot water heater can be energized and tested. It is advantageous, therefore, to provide an override mechanism for load control means that is easy to access and use.
Although the above discussion uses a hot water heater as an example of a device controlled by load control mechanisms, it should be understood that many other devices could be controlled. The present invention is not limited to use with load control mechanisms for hot water heaters.